The present invention refers generally to a plate heat exchanger, in particular a plate heat exchanger in the form of an evaporator, i.e. a plate heat exchanger designed for evaporation of a cooling agent for various applications, such as air conditioning, cooling systems, heat pump systems, etc.
A plate heat exchanger, typically includes a plate package with a plurality, of first and second heat exchanger plates which are joined to each other and arranged side by side in such a way that a first plate interspace is formed between each pair of adjacent first heat exchanger plates and second heat exchanger plates and a second plate interspace between each pair of adjacent second heat exchanger plates and first heat exchanger plates. The first plate interspaces and the second plate interspaces are separated from each other and provided side by side of each other in an alternating order in the plate package. Substantially each heat exchanger plate has at least a first porthole and a second porthole, wherein the first portholes form a first inlet channel to the first plate interspaces and the second portholes form a first outlet channel from the first plate interspaces.
The cooling agent supplied to the inlet channel of such a plate heat exchanger for evaporation is usually present both in a gaseous state and a liquid state, i.e. it is a two-phase evaporator. It is then difficult to provide an optimum distribution of the cooling agent to the different plate interspaces in such a way that an equal quantity of cooling agent is supplied and flows through each plate interspace.
DE10024888 discloses one example of a well known solution to the distribution problem wherein the inlet port of each heat exchanger plate in the plate package comprises a distributor distributing the refrigerant from the inlet channel into the plate interspaces.
DE 10 2006 002 018 discloses one example of another well known principle to the distribution problem. The refrigerant supplied to the plate heat exchanger is distributed into the inlet channel from one end thereof and further into the plate interspaces via a nozzle arrangement. Two principles are shown regarding the nozzle arrangement. In the first principle the nozzle arrangement is in the form of a plurality of small holes arranged in the circumferential, longitudinal wall portion of the inlet channel. The small holes act as spray nozzles distributing the refrigerant into the plate interspaces. In the second principle a flute is arranged to extend inside and along the inlet channel. The flute is provided with plurality of holes acting as nozzles distributing the refrigerant along the inlet channel and further into the plate interspaces.
In this general prior art plate heat exchanger the cooling agent is introduced at one end of the longitudinal first inlet channel, i.e. the first port hole, for further distribution in the form of droplets along the first inlet channel and further into each of the individual first plate interspaces. First of all it is very hard to control the flow inside the first inlet channel. There is always a risk of that the energy content of the inserted fluid is too high, whereby a part of the flow supplied to the inlet channel via its inlet port will meet the rear end of the inlet channel and be reflected thereby in the opposite direction Thereby the flow in the inlet channel is very chaotic and hard to predict and control. Further, the pressure drop of the cooling agent increases with the distance from the inlet of the first inlet channel, whereby the distribution of cooling agent between the individual plate interspaces will be affected. Thereby it is hard to optimize the efficiency of the plate heat exchanger. It is also known that the angular flow change that the droplets of the cooling agent must undergo when entering the individual plate interspaces from the first inlet channel contributes to a pressure drop.
Generally the efficiency of a plate heat exchanger at part load is a raising issue for the purpose of reducing the energy consumption. By way of example, laboratory scale trials have shown that a cooling system relating to air-conditioning may save 4-10% of its energy consumption just by improved evaporator function at part load for a given brazed plate heat exchanger. Further, an evaporator system is typically only operating at full capacity for 3% of the time, while most evaporators are designed and tuned for a full capacity operation duty. More focus is put on how the evaporator performs at different operation duties instead of being measured at only one typical operation duty. Also, the market applies so called seasonal efficiency standards. The standards may vary between different states and regions. Typically, such standards are based on a consideration including different working loads, whereby most evaporators are designed and tuned in view of a specific standard. However, during normal operation the work load varies greatly and it hardly reflects the fictive conditions used for the standard.